JPH07170203A - Squelch system for space diversity - Google Patents

Abstract

PURPOSE:To prevent the malfunction of a squelch operation when there is different path interference concerning the squelch system for space diversity for digital radio communication. CONSTITUTION:This system is composed of a converter 1 for converting a first digital multilevel modulated signal inputted from a main antenna 101 to an IF band, converter 2 for converting a second digital multilevel modulated signal inputted from a spare antenna 102 to an IF band, decision circuits 105 and 106 for inputting the output of the converter 1 or 2 and outputting the decision signal of a reception system, attenuators 103 and 104 for inputting the output of the converter 1 or 2 and the decision signal, respectively attenuating and outputting the input signals corresponding to the decided result of the decision signal, SD synthesizing board 3 for inputting the outputs of the attenuators 103 and 104, rotating the phase of an output from the attenuator 104 and synthesizing it with the output of the attenuator 103, and transmission circuit 8 for inputting the output of the SD synthesizing board 3, identifying whether that signal is a normal signal or not and performing the squelch operation when it is an interference signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a squelch system used in digital radio communication, and more particularly to a space diversity squelch system.

[0002]

2. Description of the Related Art In digital radio communication, when a signal other than a desired signal is received or the reception level is extremely lowered, in order to prevent malfunction of a transmitter / receiver after the station and to not radiate unnecessary waves , Various squelch methods have been proposed.

For example, JP-A-58-197926 and JP-A-3-58630 propose a method of performing a squelch operation by lowering a reception input level. Further, as a method of determining whether the antenna reception signal is the desired signal transmitted from the transmission side and applying squelch, there is disclosed in Japanese Patent Laid-Open No. 4-345.
229, a method of extracting a clock component,
In -116376, a method has been proposed in which a transmission side inserts a line identification signal and the reception side compares the identification signals to make a determination.

On the other hand, in digital wireless communication,
To improve the received signal level vs. thermal noise level (S / N), etc., two-sided or multi-sided space diversity (hereinafter referred to as SD) by in-phase combining
Synthesis has been adopted.

FIG. 5 shows a block diagram of a space diversity squelch system according to a conventional technique.

In the figure, 1 and 2 are reception frequency conversion boards, 3 is an SD composition board, 4 is an AGC board, 5 is a judgment circuit, and 7
Is an attenuator, 8 is a transmission circuit, 11, 24 and 83 are multipliers, 12 and 82 are (RF band) oscillators, 21 and 41 are variable attenuators, 13, 22, 25 and 42 are amplifiers, and 23 and 4 are
3, 51 are level detection circuits, 31 is a synthesis circuit, 32 is a phase shift circuit, 33 is a control signal generation circuit, 81 is a squelch circuit, 81a is an (IF band) oscillation circuit, and 10a and 10b are each (IF band) digital. An output terminal and an input terminal of the modulated signal, 101 is a main receiving antenna, 102 is a sub receiving antenna, and 100 is a transmitting antenna.

The (RF band) digital modulated signal received by the main antenna 101 is input to the reception frequency conversion board 1 and is frequency-converted from the RF band to the IF band by one output of the bifurcated (RF band) oscillator 12. , And is amplified by the amplifier 13 with a certain gain and input to the SD synthesis board 3. In addition, (RF
The other output of the band) oscillator 12 is output to the reception frequency conversion board 2.

The other output of the (RF band) oscillator 12 is controlled by the variable attenuator 21, the amplifier 22, and the detection circuit 23 so as to have a certain level, and the multiplier 2 is operated.
4 is input.

On the other hand, the (RF band) digitally modulated signal received by the sub-antenna 102 is input to the reception frequency conversion board 2 and frequency-converted from the RF band to the IF band by the multiplier 24 with a constant gain which is the amplifier 25. It is amplified and input to the SD synthesis board 3.

In the SD synthesizing board 3, the input output of the receiving frequency converting board 1 is branched into two, one of which is input to the synthesizing circuit 31 and the other of which is input to the control signal generating circuit 33. The output of the reception frequency conversion board 2 which is the other input is branched into two, one for the phase shift circuit 32 and the other for the control signal generation circuit 33.
Entered in.

The control signal generating circuit 33 outputs a control signal such that the phase difference between the two input signals becomes zero.
Output to. In addition, the phase shift circuit 33 advances (delays) the phase of the input output of the reception frequency conversion board 2 according to the output of the control signal generation circuit 33, and outputs it to the synthesis circuit 31.

The synthesis circuit 31 synthesizes the output of the reception frequency conversion board 1 and the output of the phase shift circuit 32, and outputs the synthesized signal to the AGC circuit 4 as the output of the SD synthesis board 3.

The AGC circuit 4 includes a variable attenuator 41 and an amplifier 4.
2. The detection circuit 43 controls the input signal to a certain level and outputs it to the switch 7 and the determination circuit 5.

The judgment circuit 5 is a detection circuit 51 and a discrimination circuit 5.
2, when the input signal falls below a certain prescribed level, the squelch determination signal (DET) is output to the switch 7 and (IF
The band) is output to the output terminal 10a of the digital modulation signal.

The switch 7 receives the output of the AGC circuit 4 and the squelch determination signal (DET) as input, and the squelch determination signal (DE).
If T) is the logic for operating the squelch, the output of the switch 7 is prohibited by switching the output.

The output of the switch 7 is connected to the output terminal 10a of the (IF band) digital modulation signal. The (IF band) digitally modulated signal output terminal 10a is normally connected to a modulator / demodulator and demodulates and reproduces the data signal sent on the transmitting side. It also modulates the data signal to be transmitted (IF band)
The digital modulation signal is output to the input terminal 10b.

In the case of a non-regenerative repeater station, the output terminal 10a and the input terminal 10b of this (IF band) digital modulated signal are connected as they are.

The squelch circuit 81 receives the (IF band) digital modulation signal from the input terminal 10b and the squelch determination signal (DE).
When the determination signal (DET) is a logic for operating the squelch, the (IF band) oscillation circuit 81
The output of a is selected and output to the multiplier 83.

The multiplier 83 frequency-converts the input signal into the RF band by the output of the (RF band) oscillator 82 and outputs it to the transmitting antenna.

[0020]

In the space diversity squelch method described above, since the squelch condition is determined by the signal after SD synthesis, the main antenna 10
When an unwanted wave (interference wave) is input to either the antenna 1 or the sub antenna 102, there is a problem that the SD synthesis control does not operate normally due to the difference in level between the desired wave and the unwanted wave.

Further, for example, the desired wave is transmitted to the main antenna 101,
When the unwanted wave is received by the auxiliary antenna 102, if the level of the unwanted wave is changed while keeping the input level of the desired wave constant, the input level of the unwanted wave is higher than the input level of the desired wave in the area A of FIG. Is also large, it is in the squelch operating region. In this area, if only the main antenna 101 is output, the line can be repaired but the line is disconnected.

[0022]

In the space diversity squelch system according to the present invention, the first digital multi-level modulation signal input from the main antenna is used as an input.
The digital multilevel modulation signal of the RF band (Radio Fre
frequency) to IF band (Intermediate)
Frequency), a second digital multilevel modulation signal input from an auxiliary antenna, and a carrier wave from the converter 1 as input, and the second digital multilevel modulation signal from the RF band to an IF. Converter 2 to convert to obi
And a discrimination means for discriminating whether or not the signal level of a certain band exceeds a threshold value by using the output of the converter 1 or 2 as an input, and the discrimination result corresponds to the judgment signal 1 or 2 of the corresponding receiving system. Determination circuit 1 and determination circuit 2 for outputting
And an attenuator 1 or 2 that receives the output of the converter 1 or 2 and the determination signal 1 or 2 as input and attenuates and outputs the input signal according to the determination result of the determination signal 1 (or 2), The outputs of the attenuators 1 and 2 are input, the phase of the output of the attenuator 2 is rotated based on a control method by the phase rotation means, and the output of the attenuator 1 is combined with S.
It is composed of a D synthesizer 1 and a transmitter which receives the output of the SD synthesizer 1 as an input and discriminates whether or not the signal is a normal signal and performs a squelch operation in the case of an interference signal.

[0023]

1 shows an embodiment of a space diversity squelch system according to the present invention.

Conventional Example Circuits having the same configurations as in FIG. 5 are designated by the same reference numerals. Switches 103 and 104 and determination circuits 105 and 106 are provided at the outputs of the reception frequency conversion boards 1 and 2, respectively.

A case where an interference wave (FM wave or the like) from a different path or different system is input to the main antenna 101 will be described.

The different path or different system interference wave input to the main antenna 101 is frequency-converted into the IF band by the multiplier 11 and the (RF band) oscillator 12. The frequency-converted signal is amplified by the amplifier 13 with a constant gain and input to the attenuator 103 and the determination circuit 105. Judgment circuit 1
Reference numeral 05 includes 61 bandpass filters, 63 detectors, and 64 discriminators.

The signal input to the decision circuit 105 is band-limited by the band-pass filter 61, and its level is detected by the detector 63. When the interference wave is the FM wave, most of its power is concentrated near the carrier frequency, but the multilevel digital modulated wave is spread over a wide band. Therefore, the bandpass filtering circuit 61
If the pass band of F is set near its transmission frequency, the output voltage of the detector 63 becomes larger than that of the desired digitally modulated signal.
It can be determined that it is an M signal. At this time, the determination circuit 105
The output squelch determination signal (DET1) outputs to the switch 103 a signal that the input signal is an interference wave, for example, as a logic level “H”.

The switch 103 uses the squelch determination signal (D
When ET1) is'H ', the output of the reception frequency conversion board 1 is turned off.

Therefore, only the desired wave (digitally modulated signal) received by the sub-antenna is input to the SD synthesizer board 3, and it is output as it is, so that the squelch judgment is not made by the judgment circuit 5 and the switch 7 is operated. Instead, the desired wave (digital modulation signal) is output and the line operates normally.

Even when an interference wave (FM wave or the like) from a different path or a different system is input to the sub-antenna 102, the determination circuit 106 performs the same operation as described above and the squelch determination signal (D).
ET2) is output, the switch 104 prohibits the output of the reception signal of the sub antenna 102, and the main antenna 1
Only the reception signal of 01 is input. The determination circuit 106
Has the same configuration as the determination circuit 105.

The above-mentioned inconvenience for outputting the reception signal of the main antenna 101 as shown in FIG. 4 is improved.

Both antenna inputs are unwanted waves (interference waves)
In this case, both switching devices 103 and 104 prohibit the output, so that the determination circuit 5 operates the normal squelch function.

Further, since both attenuators 103 and 104 do not operate when a desired wave is input to both antennas, the effect of normal SD synthesis can be expected.

In this embodiment, the case of the two-sided space diversity configuration has been described. However, even in the case of the space diversity configuration using N antennas (an integer of N ≧ 3), each antenna has The same effect can be expected by providing a decision circuit and an attenuator correspondingly.

In the present embodiment, the case where SD synthesis is performed in the IF band has been described. As a second embodiment, an example in which the phase shift circuit 24 is provided in the RF band to perform SD synthesis is shown in FIG. Show.

In the figure, the reception frequency conversion board 9 has an RF
Even when the phase shift circuit 24 is provided in the band, the reception frequency conversion board 9
The squelch operation is the same as in the case of FIG.

FIG. 3 shows another embodiment of the decision circuits 105 and 106 shown in FIGS. That is, the present invention relates to a determination circuit when the interference wave to be identified is an interference wave from a different route. In this case, there are two methods of inserting a route identification signal on the transmitting side, demodulating the identification signal on the receiving side and making a comparison with the route of the own station for determination, and a method of extracting a clock signal.

The determination circuit when the identification signal is inserted on the first transmitting side will be described. As a method for transmitting this identification signal, an identification signal (N-bit binary signal)
The tone signal which is the FSK is modulated by ASK (Analog
FM as gue Service Channel)
There is a means to transmit by modulation.

The identification signal transmitted as ASC can be judged by the judgment circuit shown in FIG. That is, different path interference can be determined by demodulating the ASC modulation signal with the ASC demodulation board 60, extracting the FSK modulation signal band with the band filter 62, and detecting the output with the wave detector 63.

FIG. 4 shows an embodiment of the decision circuit based on the second clock extraction. The squelch operation is the same as in the case of FIG.

In the case of a digital modulation signal, since it has a bandwidth corresponding to the frequency of the clock, the input signal is 65
When the signal which is delayed by a certain time in the delay circuit and is subjected to the multiplication processing 67 with the signal without delay is detected, its frequency component can be extracted. In the case of FM waves, it can be determined that they are interference waves because they do not have such a clock component.
Further, in the case of this determination circuit, it is possible to identify other digital modulated signals having different clock frequencies. The squelch operation is the same as in the case of FIG.

[0042]

According to the squelch method of space diversity of the present invention, the presence or absence of interference of other systems is discriminated from the input signals from the main antenna and the sub-antenna, and in the case of interference of other systems, the input of SD combination is prohibited. Therefore, when the unwanted wave is received by either the main antenna or the sub antenna, the SD synthesis control does not malfunction due to the difference in the levels of the desired wave and the unwanted wave, and the desired wave is received. Do not squelch to disconnect the line.

Further, since the squelch operation is performed by identifying the input level after SD synthesis, the SD synthesis effect can be sufficiently exerted when both antennas receive the desired wave.

If both antennas are unwanted waves, squelch operation of not outputting the unwanted waves can be expected.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing another embodiment of the present invention.

FIG. 3 is a block diagram of an implementation of a decision circuit of the present invention.

FIG. 4 is a block diagram of another embodiment of the determination circuit of the present invention.

FIG. 5 is a block diagram of a conventional example.

FIG. 6 is a diagram showing a conventional squelch operation region.

[Explanation of symbols]

1,2,9 Reception frequency conversion board 1 (and 2) 3 SD synthesis board 4 AGC board 5,105,106 Judgment circuit 7,103,104 Switcher 8 Transmission circuit 10a (IF band) Digital modulation signal output terminal 10b (IF band) Digital modulation signal input terminal 11,25,67,83 Multiplier 12,82 (RF band) Oscillator 13,22,25,42 Amplifier 21,41 Variable attenuator 23,43,51,63 Level detection Circuit 24, 32 Phase shift circuit 31 Synthesis circuit 33 Control signal generation circuit 52, 64 Identification circuit 60 ASC demodulation circuit 61, 62, 66 Band pass filter (BPF: Ba)
nd Pass Filter) 62b Multiplication circuit 63 Detection circuit 65 Delay circuit 81 Squelch circuit 81a (IF band) oscillation circuit

Claims (5)

[Claims] 1. A plurality of frequency converters for converting RF signals received by a main antenna and one or more auxiliary antennas into IF signals respectively, and a switch and a discriminator at the outputs of the plurality of frequency converters. Means for disconnecting the output of each frequency converter based on the discriminator, and controlling the phase of the output signal of the switching device connected to the output of the frequency converter connected to the auxiliary antenna to control the phase of the main signal. A space diversity squelch method comprising: a phase combining means for performing in-phase combination with the antenna side; and a means for detecting an interference signal at the output of the phase combining means and performing a squelch operation. 2. The discriminator according to claim 1, wherein the output of a narrow band filter centering on the IF center frequency is detected and a predetermined threshold value is used for the determination. . 3. The space according to claim 1, wherein the discriminator receives a signal modulated by an identification signal, demodulates the signal, and then makes a determination with a predetermined threshold value via a bandpass filter. Diversity squelch method. 4. The space diversity squelch method, wherein the determination circuit according to claim 1 determines whether or not a received signal is an interference signal by detecting a clock signal of an input signal. 5. The phase synthesizing means according to claim 1, wherein the local oscillator signal of the frequency converter of the main antenna is input and frequency conversion of the signal connected to the auxiliary antenna is performed. Space diversity squelch method characterized by controlling the phase.